Subsea wells need maintenance and inspection activities at a regular basis. Such activities can be carried out by means of tools delivered to the well via a wire or coiled tubing that extends from a floating vessel or a platform down into the well. A coiled tubing typically is a continuous and flexible tubing. The coiled tubing may be made of a metallic material or a corresponding material, such as composites. Typical maintenance and inspection activities in the well are measurements and monitoring of well conditions, perforating, gravel packing, production stimulation and repair of a downhole completion or production tubing.
The open sea represents a harsh environment where wind and wave action can greatly alter the position of a ship from one moment to the next. Movement of the open water workover riser surface flowhead due to vessel movement complicates rig-up of well workover equipment on top. A riser is a pipe that extends from the vessel to a subsea x-mas tree on the top of the well head, via which a wire or coiled tubing is fed down into the well. This is particularly an issue with rig up of coiled tubing (CT), where the equipment is heavy. Rig up/rig down involves deploying/retracting a coiled tubing/toolstring, which might be difficult upon heaving motion of the vessel.